Metallic ion source including plurality of electron guns



Aug. 18, 1970 Y J. c. PELTON, JR., E 3,525,013

METALLIC ION SOURCE INCLUDING PLURALITY 0F ELECTRON GUNS Filed July 2a, 1968 JAY c. PELTON JR. RICHARD c. sENER AGENT United States Patent 3,525,013 METALLIC ION SOURCE INCLUDING PLURALITY 0F ELECTRON GUNS Jay C. Pelton, Jr., Endicott, and Richard C. Senger, Binghamton, N.Y., assignors to International Business Machines Corporation, Armonk, N.Y.', a corporation of New York Filed July 26, 1968, Ser. No. 747,916 Int. Cl. H011 3/18, 37/08 US. Cl. 315-111 5 Claims ABSTRACT OF THE DISCLOSURE A metallic ion source including a metal vaporizer which produces uncharged metal atoms, which are directed into an ionization chamber, where two or more electron guns are positioned to direct streams of electrons into the chamber to ionize the metal atoms. The charged atoms are subjected to voltage differentials which propel them toward an ion capture chamber. Once the ions are within the ion capture chamber, they are accelerated by another voltage field. Non-ionized atoms are captured on screens provided for that purpose.

BACKGROUND OF THE INVENTION SUMMARY OF INVENTION The present invention is directed to an improved metallic ion source which will produce isolated metallic ions and the output of which source is completely controllable particularly with respect to the velocity of the emerging metallic ions.

A principal object of the invention is to provide an improved metallic ion source for producing isolated metallic ions at controllable velocities. Another object of the invention is to provide a metallic ion source which is relatively inexpensive to constuct, and small in size so that it can be accommodated in relatively small vacuum chambers. Another object of the invention is to provide a metallic ion source utilizing an appropriate arrangement of electric fields with rotational symmetry tor direct the ions in the desired direction.

A still further object of the invention is to provide a metallic ion source with provisions for decelerating the ions once they have been given an initial direction so that the ions at the output are moving at a relatively low velocity.

Another object of the invention is to provide an improved metallic ion source which prevents distortion of the controlling electric ifields as a result of build-up of metal on the electrodes in the fields.

In practicing the invention, uncharged metal atoms are produced in a. suitable sounce, such as a metal evaporator, and are spewed into an ionization chamber having a rotational symmetry around a particular axis. Two or more electron beams are directed through the ionization chamber at angles with respect to the axis of the chamber to thereby direct the streams of electrons into the metallic atoms and cause ionization thereof. As the ions are created, they are influenced by an electrical field which ice directs them through an opening in an accelerating electrode at the end of the chamber. They then enter a deceleration chamber maintained at a potential such that the ions are slowed down to a suitable velocity as they leave the chamber. The ionizing electron beams are di rected to strike targets which are exterior to the ionization chamber itself, thus avoiding secondary emission effects within the chamber. The acceleration electrode has a capture screen which faces the evaporator and the entrance to the chamber so that any un-ionized vapors are trapped and distortion of the field by build-up of metal on the acceleration electrode is prevented. By suitably controlling the potentials on the ionization chamber, the acceleration electrode, and the following deceleration chamber, the velocity of the ions as they emerge from the device can be completely controlled. A suitable number of electron guns can be used to thereby increase the eificiency of the source with respect to the number of metallic ions created versus the number of metallic vapor atoms produced.

DESCRIPTION OF THE DRAWINGS The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of a preferred embodiment of the invention, as illustrated in the accompanying drawings.

In the drawings:

FIG. 1 shows, in diagrammatic form, a plan view of an ionization chamber constructed in accordance with the preferred embodiment of the present invention, partially cut away to show certain of the interior details.

FIG. 2 is a schematic illustration of the ionization chamber assembly as viewed looking toward the ionization chamber from the metallic ion source.

Similar reference characters refer to similar parts in each of the views.

Uncharged metal atoms are produced in a suitable metal evaporator 1, which may be of any type that produces a cloud of uncharged metallic atoms, as by vaporization of the appropriate metal by electrical resistance heating, for example. The uncharged metal atoms are spewed out of the metal evaporator and enter the ionization chamber 3, via an opening in the cover plate *5. Chamber 3 is conical in form for reasons to be subsequently explained. The cover plate 5, as well as the ionization chamber 3 are maintained at some potential provided by a source such as the battery 7 shown, connected to a voltage divider 9. Cover plate 5 and ionization chamber 3 are held at the same potential since they are electrically connected. An acceleration electrode 11 mounted in an insulating supporting ring 13 at the exit end of the chamber 3 is connected as shown in the drawing to be held at some potential which is negative with respect to the potential of the ionization chamber and cover plate.

A pair of electron guns 15 and 15' are mechanically connected to the ionization chamber and are arrayed in the manner shown in the drawings so that each electron gun directs a stream of electrons into the ionization chamber through a "suitable opening in the sidewall of the chamber. These electron beams provide a supply of electrons which mingle with the incoming metallic atoms and cause ionization of the atoms. The electron beams are aligned in such a, way as to exit through the cover plate 5 through appropriate openings such as the slot 17, seen in FIG. 2, so that the electron beams finally impinge on associated target electrodes 19 and 19.

It will be noted that the target electrodes 19 and 19' are outside of the ionization chamber per se, and as shown diagrammatically, are connected into the circuitry of the electron guns 15 and 15' to afford the usual configuration of target electrodes for the impinging electron beams. By placing the target electrodes outside of the ionization chamber, any secondary emission effects which take place as a result of the electron stream striking the targets will take place outside of the ionization chamber and will not interfere with the ionization of the atoms in the chamber. It should be noted that the alignment of the electron guns, the targets and the slots for the beams is such that the beams do not intersect, but rather cross over one another at a point on the axis of the ionization chamber, so that there is no interaction of one electron beam with the other.

Although only two electron beams and two associated electron guns are illustrated, more beams may be provided by arranging additional electron guns around the periphery of the ionization chamber, to thereby increase the number of metallic ions produced with respect to the amount of vapor that is supplied to the chamber.

The rotational symmetry of the ionization chamber 3 along with its tapered dimension along the axis of the chamber and symmetrical arrangement of the electron beams about the axis of the chamber provide an arrangement which focuses or collimates the metallic vapors toward the opening in the acceleration electrode 11.

As a result of the electric field effects on the ions, they are collected and passed through the opening in the acceleration electrode 11 into a deceleration chamber 21, which is maintained at a positive potential with respect to the acceleration electrode 11 as indicated by the connections in the diagram. It will be apparent to those skilled in the art that by altering the shape of the deceleration chamber 21 and by changing the potential thereon with respect to the acceleration electrode 11, the ions may be further accelerated if desired rather than decelerated.

The acceleration electrode 11 has a capture screen incorporated therein which faces the evaporator 1 in order to trap any vapors which are un-ionized. This arrangement prevents distortion of the field resulting from build up of metal on the acceleration electrode itself. By suitable control of the output of the metal evaporator 1 and by further controlling the potentials applied to the chamber and the currents of the electron guns, the output of the ion source is controllable and the velocity of the charged ions leaving the exit end of the decelerating chamber 21 may be effectively controlled so that the ions are moving with little or no velocity, for example, at the time they exit chamber 21.

From the foregoing, it will be apparent that the present invention provides an improved metallic ion source which permits the generation of isolated metallic ions having a controlled velocity which may be rendered very low, for use in vacuum deposition processes. The apparatus is advantageous from the standpoint of economy of manufacture and small relative size.

While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. A metallic ion source comprising, in combination,

(a) a metallic vapor source for producing uncharged metal atoms,

(b) an ionization chamber having an entrance opening and an exit opening each centered on a axis extending through the chamber, said chamber having a rotational symmetry about said axis, said metallic vapor source being located in proximity to said entrance opening to supply uncharged metal atoms to said chamber,

(c) at least two electron guns arranged symmetrically around the axis of said ionization chamber, each gun effective to supply a stream of electrons into said chamber, said stream converging toward a locus about the axis of said chamber and in proximity to said entrance opening, to thereby ionize the metal atoms entering said chamber (d) an accelerating electrode located at the exit opening of said chamber, and

(e) potential supply means for establishing electrical potentials between said chamber and said electrode for accelerating ions in said chamber toward said exit opening.

2. A metallic ion source as claimed in claim 1, further including a deceleration chamber adjacent said ionization chamber and aligned with the axis of said ionization chamber, and means for establishing a potential difference between said ionization chamber and said deceleration chamber.

3. A metallic ion source as claimed in claim 1, further characterized by including a plurality of target electrodes, one for each of said electron guns, said target electrodes being located eXteriorly of said ionization chamber, and at least one opening in said chamber to permit the electron beams from said electron guns to leave said chamber and impinge upon said target electrodes.

4. A metallic ion source as claimed in claim 1, further characterized by said ionization chamber having the form of a truncated cone, with said entrance opening in the base of the conical form.

5. A metallic ion source as claimed in claim 2, further characterized by said deceleration chamber having the form of a truncated cone with the base adjacent said ionization chamber.

References Cited UNITED STATES PATENTS 2,883,568 4/1959 Beam et al 313-230 X 2,911,531 11/1959 Rickard et a1. 25041.9 2,928,943 3/1960 Bartz et a1. 313-63 X 3,409,529 11/1968 Chopra et a1. 3l3-63 X JAMES W. LAWRENCE, Primary Examiner P. C. DEMEO, Assistant Examiner U.S. Cl. X.R. 

